Simultaneous time domain differential sensing and electric field sensing

ABSTRACT

Systems and methods for determining a touch input are provided. The systems and methods generally include measuring the peak voltage at an electrode over a measurement period and determining a touch input based on the peak voltage. The systems and methods can conserve computing resources by deferring digital signal processing until after a peak electrode capacitance has been sampled. The systems and methods are suitable for capacitive sensors using self-capacitance and capacitive sensors using mutual capacitance. The systems and methods are also suitable for capacitive buttons, track pads, and touch screens, among other implementations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Application No. 61/947,641,filed Mar. 4, 2014, and 2015 Mar. 4 Priority to PCT/US2015/018593, andU.S. application Ser. No. 15/122,541 the disclosure of which isincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to systems and methods for detecting atouch input.

Touch inputs are widely used as an input methodology. For example, touchinputs are used in conjunction with appliances, tablets, andsmartphones. Touch inputs can be determined based on a capacitive outputof an electrode. According to one known method, the value of thecapacitive output is used to determine the presence of a touch input ona substrate or the location of a touch input on a two-dimensional panel.

FIG. 1 illustrates a known circuit for detecting a touch input usingself-capacitance. The circuit includes a measurement circuit and asignal processing circuit. The measurement circuit includes a voltagesource (Vdd), electrodes for eight capacitive buttons (Ce1, Ce2 . . .Ce8), and a sampling capacitor (Cs). Each electrode is independentlysampled. The output of each electrode is forwarded to the signalprocessing circuit. The signal processing circuit includes an amplifier,an analog-to-digital converter, and a time domain differential signatureprocessing circuit. The signal processing circuit includes an outputresponse, for example a digital signal indicative of the time of a touchinput at one of the eight capacitive buttons.

FIG. 2 illustrates another known circuit for detecting a touch inputusing mutual-capacitance. The circuit of FIG. 2 includes the signalprocessing circuit of FIG. 1, however the measurement circuit ismodified to include an electrode pairing for each of the eightcapacitive buttons. The voltage source (Vdd) provides a stimulus voltageto sequential ones of the electrode pairings. The output of eachelectrode pairing is forwarded to the signal processing circuit. Thesignal processing circuit amplifies each output before converting eachoutput into a digital signal for time domain differential processing.The output response includes a digital signal indicative of the time ofa touch input at one of the eight capacitive buttons.

The circuits of FIGS. 1-2 digitally process each electrode outputsampled by the measurement circuit. This scheme is potentiallyburdensome, particularly if rapid measurements are required for the timedomain differential processing circuit. Accordingly, there remains acontinued need for circuits and methods that rapidly measure electrodecapacitance while minimizing computing resources, optionally for use inconjunction with time domain differential processing methods.

SUMMARY OF THE INVENTION

Systems and methods for determining a touch input are provided. Thesystems and methods generally include measuring the peak voltage at anelectrode over a measurement period and determining a touch input basedon that peak voltage. The systems and methods can conserve computingresources by deferring digital signal processing until after a peakelectrode capacitance has been sampled. The systems and methods aresuitable for capacitive sensors using self-capacitance and capacitivesensors using mutual capacitance. The systems and methods are alsosuitable for capacitive buttons, track pads, and touch screens, amongother implementations.

According to one embodiment, the system includes a capacitive sensor forreceiving a touch input. The capacitive sensor includes a drivercircuit, a measurement circuit, and a signal processing circuit. Thedriver circuit is adapted to providing a stimulus voltage, for example arepeating square wave, to a capacitive coupling. The measurement circuitincludes a peak detector and provides an output proportional to the peakvoltage across the capacitive coupling over a measurement period. Thesignal processing circuit is then adapted to process the peak voltage indigital logic to determine the presence or absence of a touch input on atouch substrate of the capacitive sensor.

According to another embodiment, the measurement circuit includes astrobe electrode and a sense electrode defining a capacitive couplingtherebetween, the capacitive coupling being adapted to vary in responseto a touch input. The driver circuit is adapted to provide a repeatingstimulus voltage to the strobe electrode over a measurement period. Themeasurement circuit includes a peak detector electrically coupled to thesense electrode. The peak detector is adapted to measure the peakvoltage over the same measurement period for output to a signalprocessing circuit.

According to still another embodiment, the measurement circuit includesa plurality of electrode pairs, each including a strobe electrode and asense electrode, and a corresponding plurality of peak detectors. Themeasurement circuit is adapted to simultaneously sample the peak voltagefor each of the electrode pairs, and to subsequently forward the peakvoltage for the desired electrode pair to the signal processing circuit.The signal processing circuit optionally includes a time domaindifferential processing circuit to determine the rate of change of theoutput of the measurement circuit, which can then be used to determinethe presence of a touch input.

According to yet another embodiment, the measurement circuit includes asingle strobe electrode and a plurality of sense electrodes. The strobeelectrode is capacitively coupled to the plurality of sense electrodesto define a plurality of capacitive couplings. The measurement circuitadditionally includes a peak detector for each of the sense electrodes,the peak detectors being adapted to simultaneously sample the peakvoltage for each capacitive coupling over a measurement period. Themeasurement circuit is further adapted to forward the peak voltage forthe desired capacitive coupling to the signal processing circuit. Thesignal processing circuit optionally includes a time domain differentialprocessing circuit to determine the rate of change of the output of themeasurement circuit, which can then be used to determine the presence ofa touch input.

According to even another embodiment, the signal processing circuitdetects a touch input by determining the rate of change of electrodecapacitance. The rate of change of electrode capacitance can decrease,slowing to nearly zero, as an object comes to rest against a touchsurface. As the rate of change of electrode capacitance falls below athreshold value, a touch condition is registered. The touch conditioncan correspond to the object coming to rest, or very nearly to rest, forexample the placement and flattening of a fingertip against a touchsubstrate. The signal processing circuit can additionally include anamplifier coupled to the output of the measurement circuit and ananalog-to-digital converter coupled to the output of the amplifier.

These and other features and advantages of the present invention willbecome apparent from the following description of the invention, whenviewed in accordance with the accompanying drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a prior art capacitive touch sensorincluding eight capacitive buttons using self-capacitance;

FIG. 2 is a circuit diagram of a prior art capacitive touch sensorincluding eight capacitive buttons using mutual-capacitance;

FIG. 3 is a circuit diagram of a capacitive touch sensor in accordancewith a first embodiment;

FIG. 4 is a first timing diagram of the capacitive touch sensor of FIG.3;

FIG. 5 is a second timing diagram of the capacitive touch sensor of FIG.3;

FIG. 6 is a third timing diagram of the capacitive touch sensor of FIG.3;

FIG. 7 is a circuit diagram of a capacitive touch sensor in accordancewith a second embodiment;

FIG. 8 is a timing diagram of the capacitive touch sensor of FIG. 7;

FIG. 9 is a circuit diagram of a capacitive touch sensor in accordancewith a third embodiment;

FIG. 10 is a first timing diagram of the capacitive touch sensor of FIG.9;

FIG. 11 is a second timing diagram of the capacitive touch sensor ofFIG. 9;

FIG. 12 is a third timing diagram of the capacitive touch sensor of FIG.9;

FIG. 13 is a circuit diagram of a capacitive touch sensor in accordancewith a fourth embodiment;

FIG. 14 is a timing diagram of the capacitive touch sensor of FIG. 13;

FIG. 15 is a circuit diagram of a capacitive touch sensor in accordancewith a fifth embodiment;

FIG. 16 is a first timing diagram of the capacitive touch sensor of FIG.15;

FIG. 17 is a second timing diagram of the capacitive touch sensor ofFIG. 15;

FIG. 18 is a third timing diagram of the capacitive touch sensor of FIG.15;

FIG. 19 is a circuit diagram of a capacitive touch sensor in accordancewith a sixth embodiment;

FIG. 20 is a timing diagram of the capacitive touch sensor of FIG. 19;

FIG. 21 is a circuit diagram of a capacitive touch sensor in accordancewith a seventh embodiment;

FIG. 22 is a first timing diagram of the capacitive touch sensor of FIG.21;

FIG. 23 is a second timing diagram of the capacitive touch sensor ofFIG. 21;

FIG. 24 is a third timing diagram of the capacitive touch sensor of FIG.21;

FIG. 25 is a circuit diagram of a capacitive touch sensor in accordancewith an eighth embodiment;

FIG. 26 is a timing diagram of the capacitive touch sensor of FIG. 25;

FIG. 27 is a circuit diagram of a capacitive touch sensor in accordancewith a ninth embodiment;

FIG. 28 is a first timing diagram of the capacitive touch sensor of FIG.27;

FIG. 29 is a second timing diagram of the capacitive touch sensor ofFIG. 27;

FIG. 30 is a third timing diagram of the capacitive touch sensor of FIG.27;

FIG. 31 is a circuit diagram of a capacitive touch sensor in accordancewith a tenth embodiment;

FIG. 32 is a timing diagram of the capacitive touch sensor of FIG. 31;

FIG. 33 is a circuit diagram of a capacitive touch sensor in accordancewith an eleventh embodiment;

FIG. 34 is a first timing diagram of the capacitive touch sensor of FIG.33;

FIG. 35 is a second timing diagram of the capacitive touch sensor ofFIG. 33;

FIG. 36 is a third timing diagram of the capacitive touch sensor of FIG.33;

FIG. 37 is a circuit diagram of a capacitive touch sensor in accordancewith a twelfth embodiment;

FIG. 38 is a timing diagram of the capacitive touch sensor of FIG. 37;

FIG. 39 is a circuit diagram of a capacitive touch sensor in accordancewith a thirteenth embodiment;

FIG. 40 is a first timing diagram of the capacitive touch sensor of FIG.39;

FIG. 41 is a second timing diagram of the capacitive touch sensor ofFIG. 40;

FIG. 42 is a third timing diagram of the capacitive touch sensor of FIG.41;

FIG. 43 is a circuit diagram of a capacitive touch sensor in accordancewith a fourteenth embodiment;

FIG. 44 is a timing diagram of the capacitive touch sensor of FIG. 43;

FIG. 45 is a depiction of eight single-electrodes for use with theforegoing embodiments using self-capacitance;

FIG. 46 is a depiction of eight dual-electrodes for use with theforegoing embodiments using mutual-capacitance;

FIG. 47 is a depiction of eight dual-electrodes for use with theforegoing embodiments using self-capacitance with atransistor-electrode-pair;

FIG. 48 is a depiction of eight dual-electrodes for use with theforegoing embodiments using mutual-capacitance with atransistor-electrode-pair; and

FIG. 49 is a circuit diagram of a capacitive touch sensor in accordancewith a fifteenth embodiment.

DESCRIPTION OF THE CURRENT EMBODIMENTS

The current embodiments generally relate to systems and methods fordetermining a touch input. The systems and methods generally includemeasuring the peak voltage at an electrode over a measurement period anddetermining a touch input based on the peak voltage. The systems andmethods can conserve computing resources by deferring digital signalprocessing until after a peak voltage has been measured. The systems andmethods are suitable for capacitive sensors using self-capacitance andcapacitive sensors using mutual capacitance. The systems and methods arealso suitable for capacitive buttons, track pads, and touch screens,among other implementations. In addition, the systems and methods can beimplemented in conjunction with the sensing circuits set forth inWO2010/111362 to Caldwell et al entitled “Apparatus and Method forDetermining a Touch Input,” and WO2013/163496 to Caldwell et al entitled“Apparatus and Method for Determining a Stimulus, Including a TouchInput and a Stylus Input,” the disclosures of which are incorporated byreference in their entirety.

Referring now to FIG. 3, a circuit diagram for a capacitive sensor inaccordance with a first embodiment is illustrated. The capacitive sensorincludes a driving circuit 12, a measurement circuit 14, and a signalprocessing circuit 16. The driving circuit 12 includes a voltage source(Vdd) that is adapted to provide a stimulus voltage, for example therepeating 3V square shown in FIG. 4. The voltage source is optionallycontrolled by a controller, for example an ASIC, an FPGA, or amicrocontroller, which also controls operation of the switches in FIG.3. The measurement circuit 14 additionally includes a measurementcapacitor (Ce), and in particular a strobe electrode capacitivelycoupled to a sense electrode. The measurement capacitor (Ce) includes acapacitance that changes depending on the presence or absence of touchinput on a nearby touch substrate. For example, when “no touch” ispresent, the measurement capacitor (Ce) may have a lower value ofcapacitance than when a “touch” is present. Likewise, when a “touch” ispresent, the measurement capacitor (Ce) may have a higher value ofcapacitance.

The measurement circuit 14 additionally includes a peak detector 18. Thepeak detector 18 is adapted to output a DC voltage proportional to thepeak value of the AC voltage across the measurement capacitor (Ce). Thepeak detector 18 includes a peak detector diode (Ds), a peak detectorcapacitor (Cs), and a gate switch (SwB), the diode (Ds) and thecapacitor (Cs) being connected in series to ground. The diode (Ds)conducts positive half cycles, charging the capacitor (Cs) to thewaveform peak. When the input waveform falls below the DC peak stored tothe capacitor (Cs), the diode (Ds) is reverse biased, blocking currentflow from the capacitor (Cs) to the capacitor (Ce). Thus, the capacitor(Cs) retains the peak value even when the waveform drops to zero. Statedsomewhat differently, the peak detector 18 generally includes an analogmemory, for example the capacitor (Cs), to store a charge proportionalto the peak value of the voltage across the measurement capacitor (Ce).The peak detector 18 additionally includes a unidirectional switch, forexample the diode (Ds), to charge the capacitor (Cs) when a new peakarrives at the input of the peak detector. The peak detector 18additionally includes a switch to periodically reinitialize the outputto zero, for example the gate switch (SwB), at the end of themeasurement cycle. As further shown in FIG. 4, exemplary stimulusvoltage (VStimulus) includes a repeating 3V square wave. The voltageacross the capacitor (Vin) and the voltage at the peak detectorcapacitor (Vpkd) is also shown in FIG. 4. The voltage at the peakdetector capacitor (Cs) can take several cycles to charge to the peakdue to the series resistance (RC time constant).

Referring again to FIG. 3, the measurement circuit 14 includes anelectrostatic suppression resistor (Resd) and a load resistor (RL) todischarge parasitic capacitance. The load resister (RL) may be used toprovide a lower impedance path or to attenuate the output from thedriving circuit 12, such that the waveform can be attenuated prior todetecting a peak voltage at the peak detector capacitor (Cs). Themeasurement circuit additionally includes a sample-and-hold capacitor(Cadc) and a discharge switch (SwA). The gate switch (SwB) and thedischarge switch (SwA) are operatively coupled to the same controllerthat controls operation of the voltage source (Vdd). When the gateswitch (SwB) is closed and the discharge switch (SwA) is open, the DCoutput of the peak detector 18 is provided to the signal processingcircuit 16. When the gate switch (SwB) is open and the discharge switch(SwA) is closed, the sample-and-hold capacitor (Cadc) is discharged toground for the subsequent measurement cycle. Each measurement cycle caninclude two or more cycles of the repeating waveform, such that the peakvoltage is selected from among at least two available ‘peaks’ of an ACsignal. The measurement cycle can include 10 microseconds in someembodiments, such that a peak voltage is provided to the signalprocessing circuit 16 every 10 microseconds. The measurement cycle caninclude other durations in other embodiments where desired.

The signal processing circuit 16 includes an analog-to-digital converter(ADC), a Time Domain Differential Processing Circuit, and an OutputResponse. The ADC converts the analog DC output of the measurementcircuit 14 into a digital signal for processing by the Time DomainDifferential Processing Circuit. The Time Domain Differential ProcessingCircuit can perform the processing steps set forth in WO2010/111362 toCaldwell et al entitled “Apparatus and Method for Determining a TouchInput,” and WO2013/163496 to Caldwell et al entitled “Apparatus andMethod for Determining a Stimulus, Including a Touch Input and a StylusInput.” The processing steps are generally programmed into computerreadable memory that, when executed, cause a processor to determine thepresence or absence of a stimulus, for example a touch input or a touchsignature. The instructions that are performed by the processor aregenerally stored in a computer readable data storage device. Thecomputer readable data storage device can be a portable memory devicethat is readable by the computer apparatus. Such portable memory devicescan include a compact disk, a digital video disk, a flash drive, and anyother disk readable by a disk driver embedded or externally connected toa computer, a memory stick, or any other portable storage medium whethernow known or hereinafter developed. Alternatively, the machine-readabledata storage device can be an embedded component of a computer such as ahard disk or a flash drive of a computer. Together, the computer andmachine-readable data storage device can be a standalone device orembedded into a machine or a system that uses the instructions for auseful result. The Output Response can include a digital signalindicative of the timing of a touch input on a touch substrate. Furtherby example, the digital signal can include the touch signature,including for example the duration of the touch input, the rate at whichthe finger or stylus approached the touch substrate, and the rate atwhich the finger or stylus receded from the touch substrate. Othercharacteristics of the touch signature may be included in the OutputResponse in other embodiments where desired.

Referring now to FIGS. 5 and 6, multiple samples may be made at a fasterrate to increase signal fidelity and to reduce noise. By increasing thefrequency of the AC stimulus voltage, signal to noise ratio isincreased, the response time is decreased (due to a faster sampling ratethat is not limited by an ADC conversion time), resulting in a decreasedpower draw (less digital processing and ADC operation). An amplifier maybe added to the signal processing circuit 16, which can further decreasethe response time (less ADC samples to achieve an increased signallevel) and decrease power draw (less digital processing and ADCoperation provided amplifier is a low power amplifier).

In the interest of clarity, the general outline of the driving circuit12, the measurement circuit 14, and the signal processing circuit 16 arenot reproduced in the embodiments of FIGS. 7-49, but are neverthelesspresent in those drawings.

Referring to FIG. 7, a circuit diagram for a capacitive sensor inaccordance with a second embodiment is illustrated. The capacitivesensor of FIG. 7 is similar in structure and function as the capacitivesensor of FIG. 3, except that the capacitive sensor of FIG. 7 includes aplurality of measurement capacitors (Ce1, Ce2 . . . Ce8) and acorresponding plurality of peak detectors. The peak detectors include adiode (Ds1, Ds2 . . . Ds8), a peak detector capacitor (Cs1, Cs2 . . .Cs8), and a gate switch (SwB1, SwB2 . . . SwB8). The peak detectors areconnected through the gate switch (SwB1, SwB2 . . . SwB8) to thesample-and-hold capacitor (Cadc). The measurement circuit 14 canadditionally include an electrostatic suppression resistor (Resd1, Resd2. . . Resd8) and a load resistor (RL1, RL2 . . . RL3) for eachmeasurement capacitor (Ce1, Ce2 . . . Ce8). In this embodiment, themeasurement capacitor (Ce1, Ce2 . . . Ce8) includes a single strobeelectrode and eight sense electrodes. An exemplary physical constructionis depicted in FIG. 46, where the strobe electrode is depicted as“Stimulus” and the sense electrodes are depicted as Ce1, Ce2 . . . Ce8.The driving circuit 12 can simultaneously stimulate each of themeasurement capacitors (Ce1, Ce2 . . . Ce8) over the same measurementcycle. The discharge switch (SwA) is used to couple the DC output of aselected one of the peak detector capacitors (Cs1, Cs2 . . . Cs8) withthe ADC of the signal processing circuit 16. The signal processingcircuit 16 then determines which, if any, of the measurement capacitors(Ce1, Ce2 . . . Ce8) registered a touch input during the measurementcycle. If the measurement cycle is kept sufficiently small, the signalprocessing circuit 16 effectively determines the presence ofsimultaneous touch inputs using a single time domain differentialprocessing circuit, rather than a dedicated circuit for each measurementcapacitor (Ce1, Ce2 . . . Ce8).

Referring now to FIG. 8, multiple samples may be made at a faster rateto increase signal fidelity and to reduce noise. By increasing thefrequency of the AC stimulus voltage, signal to noise ratio isincreased, the response time is decreased (due to a faster sampling ratethat is not limited by an ADC conversion time), and the power draw isdecreased (less digital processing and ADC operation). An amplifier maybe added to the signal processing circuit 16, which can further decreasethe response time (less ADC samples to achieve an increased signallevel) and decrease power draw (less digital processing and ADCoperation provided amplifier is a low power amplifier). Noise will tendto cancel due to the simultaneous measurements of common mode noise.

Referring to FIG. 9, a circuit diagram for a capacitive sensor inaccordance with a second embodiment is illustrated. The capacitivesensor of FIG. 9 is similar in structure and function as the capacitivesensor of FIG. 3, except that the measurement capacitor (Ce) includes atransistor-controlled electrode for measuring self-capacitance. Inparticular, a PNP transistor (Q) includes an emitter that is coupled tothe voltage source (Vdd), a base coupled to a resistor (Rbe), and acollector coupled to the peak detector diode (Ds). In operation, themeasurement electrode (Ce) and the resistor (Rbe) form a delay network.For example, the stimulus voltage causes a voltage to develop betweenthe emitter and the base of the PNP transistor (Q), causing a basecurrent to flow. This will in turn cause collector current to flow thatis proportional to the gain of the transistor (Q). If the capacitance ofthe measurement capacitor (Ce) increases due to a stimuli, for example atouch input, the collector current will increase, which will charge thepeak detector capacitor (Cs) for a give pulse of stimulus. FIG. 10includes a timing diagram illustrating operation of the capacitivesensor of FIG. 9. The voltage (Vin) immediately prior to the peakdetector diode (Ds) rises and falls with the stimulus voltage(VStimulus) during the measurement cycle, accompanied by the charging ofthe peak detector capacitor (Cs). FIG. 11 includes the results ofrepeated pulses of sampling. After the measurement cycle, all capacitorsincluding parasitic capacitance are discharged and the process isrepeated for processing by the Time Domain Differential ProcessingCircuit, after possible amplification and analog-to-digital conversion.FIG. 12 also shows the increased response time and sensitivityattributed to the transistor (Q).

Referring to FIG. 13, a circuit diagram for a capacitive sensor inaccordance with a fourth embodiment is illustrated. The capacitivesensor of FIG. 13 is similar in structure and function as the capacitivesensor of FIG. 9, except that the capacitive sensor of FIG. 13 includesa plurality of measurement capacitors (Ce1, Ce2 . . . Ce8) and acorresponding plurality of peak detectors. Each measurement capacitor(Ce1, Ce2 . . . Ce8) is electrically coupled to a resistor (Rbe1, Rbe2 .. . Rbe8) and a PNP transistor (Q1, Q2 . . . Q8), such that themeasurement capacitor (Ce1, Ce2 . . . Ce8) and the resistors (Rbe1, Rbe2. . . Rbe8) form a delay network across the transistors (Q1, Q2 . . .Q8). Each transistor collector is coupled to a peak detector, and inparticular a peak detector diode (Ds1, Ds2 . . . Ds8) and a peakdetector capacitor (Cs1, Cs2 . . . Cs8). The peak detector capacitors(Cs1, Cs2 . . . Cs8) are connected through a gate switch (SwB1, SwB2 . .. SwB8) to the sample and hold capacitor (Cadc). The measurement circuit14 can additionally include an electrostatic suppression resistor(Resd1, Resd2 . . . Resd8) and a load resistor (RL1, RL2 . . . RL3) foreach measurement capacitor (Ce1, Ce2 . . . Ce8). In this embodiment, themeasurement capacitor (Ce1, Ce2 . . . Ce8) includes a single strobeelectrode. The driving circuit 12 can simultaneously stimulate each ofthe strobe electrodes over the same measurement cycle. The dischargeswitch (SwA) is used to couple the DC output of a selected one of thepeak detection capacitors (Cs1, Cs2 . . . Cs8) with the ADC of thesignal processing circuit 16. The signal processing circuit 16 thendetermines which, if any, of the peak detector capacitors (Cs1, Cs2 . .. Cs8) registered a touch input during the measurement cycle. FIG. 11includes the results of repeated pulses of sampling. If the measurementcycle is kept sufficiently small, the signal processing circuit 16effectively determines the presence of simultaneous touch inputs using asingle time domain differential processing circuit, rather than adedicated circuit for each peak detector capacitor (Cs1, Cs2 . . . Cs8).After the measurement cycle, all capacitors (including parasiticcapacitance) are discharged and the process is repeated for processingby the Time Domain Differential Processing Circuit, after possibleamplification and analog-to-digital conversion.

FIG. 15 illustrates an electrical schematic and block diagram of acapacitance sensor in accordance with a fifth embodiment. Timingdiagrams associated with one or more operational states of theillustrated embodiment are shown in FIGS. 16 through 18. The sensor issimilar to the sensor described in connection with the illustratedembodiment of FIG. 3, but with several differences. The sensor of FIG.15 includes a measurement circuit 14 configured to assess multiplesamples generated by the driving circuit 12, and to provide an outputindicative of a characteristic of the multiple samples, such as a peakvoltage detected across a capacitive coupling over a measurement period.The characteristic can be unique among the multiple samples generatedover the measurement period, or can be based on one or more aspects ofseveral of the multiple samples.

In the illustrated embodiment, the capacitive touch sensor of FIG. 15may include driver circuitry 12 and signal processing circuitry 16,similar to the driver circuitry 12 and signal process circuitry 16 ofFIG. 3. And, similar to the sensor of FIG. 3, the basic techniqueutilized by the capacitive touch sensor for detecting and processing atouch input includes sensing the effective net capacitance of acapacitor. For example, the measurement capacitor (Ce), including astrobe electrode and a sense electrode, may represent the effective netcapacitance of a single electrode sensing element. The effectivecapacitance seen by the sense electrode of the measurement capacitor(Ce) may change depending on the capacitance present, which furtherdepends on whether a touch is present. In other words, when “no touch”is present, the measurement capacitor (Ce) may have a lower value ofcapacitance than when a “touch” is present. Likewise, when a “touch” ispresent, measurement capacitor (Ce) may have a higher value ofcapacitance. As discussed herein, the measurement circuitry 14 mayassess the capacitance seen by the sense electrode over multiplesamples, and provide an output indicative of a characteristic of themultiple samples, such as a peak voltage detected. The signal processcircuitry 16 may evaluate the output from the measurement circuitry 14to determine whether the output is indicative of a “touch” beingpresent.

The measurement circuitry 14 of the illustrated embodiment of FIG. 15includes a peak detector that detects a peak voltage of multiple samplesof the measurement capacitor (Ce) generated by the driver circuitry. Thepeak detector may include a peak detector capacitor (Cs) and a peakdetector diode (Ds). It should be understood that, as mentioned herein,the measurement circuitry may be constructed differently and may assessmultiple samples in a different manner, such as by detecting acharacteristic of the multiple samples other than the peak voltage.Similar to the measurement circuitry of FIG. 3, the measurementcircuitry of FIG. 15 may include an electrostatic suppression resistor(Resd), an A-to-D gate switch (SwB), a sample/hold capacitor (Cadc), anda discharge switch (SwA). As discussed herein, and depicted in theillustrated embodiment of FIG. 15, parasitic capacitance may be presenton the strobe electrode, potentially adversely affecting the ability ofthe measurement circuitry to assess effective capacitance seen by thestrobe electrode. Adverse effects caused by the presence of parasiticcapacitance may impact the samples generated by the drive circuitry, andskew or distort the output generated by the measurement circuitry,potentially causing a false positive indication or a false negativeindication of a touch being present.

Adverse effects due to presence of parasitic capacitance may be reducedor eliminated using one or more of the configurations described herein.For example, in the illustrated embodiment of FIG. 3, the load resistor(RL) may be used to discharge parasitic capacitance. The load resistor(RL), as discussed herein, may be used to provide a lower impedance pathor to attenuate the output from the drive circuit (12) to themeasurement circuit (14) such that the output or sensor signal can beattenuated prior to peak detecting an accumulation of charge on the peakdetector capacitor (Cs).

In the illustrated embodiment of FIG. 15, a parasitic discharge switch(SwD) may be selectively activated to discharge parasitic capacitance.The controller can control activation of the discharge switch (SwD) sothat discharge of parasitic capacitance can be conducted at selectperiods of time rather than constantly. Optionally, the discharge switch(SwD) may be used in conjunction with a load resistor (RL) to affectparasitic capacitance. In this optional configuration, the load resistor(RL) may be used in conjunction with the discharge switch (SwD) toprovide for adjustment of lower impedances of the output from the drivecircuitry 15-102, or to attenuate the output of the drive circuitry 12prior to peak detecting an accumulation of charge, or both.

In the illustrated embodiment of FIG. 19, an electrical schematic andblock diagram of a multi-electrode capacitance sensor or an array-typecapacitance sensor is shown. A timing diagram associated with one ormore operational states of the illustrated embodiment are shown in FIG.20. With several exceptions, the capacitor touch sensor of FIG. 19 issimilar to the capacitor touch sensor of FIG. 15. In particular, thecapacitor touch sensor of FIG. 19 includes measurement circuitry that isconfigured to assess multiple samples generated by drive circuitry, andto provide an output indicative of the multiple samples to signalprocessing circuitry.

The multi-electrode capacitance sensor of FIG. 19 may operate in amanner generally similar to the multi-electrode capacitance sensor ofFIG. 7. More specifically, the voltage source (Vdd) may stimulatemultiple electrode sensing elements (Ce1, Ce2 . . . Ce8), similar to themeasurement capacitor (Ce) described in connection with the illustratedembodiment of FIG. 15. Each of the multiple electrode sensing elements(Ce1, Ce2 . . . Ce8) may be incorporated into a respective measurementstage, which, similar to the measurement circuit, may assess thecapacitance seen by a respective sensing element (Ce1, Ce2 . . . Ce8)over multiple samples generated by the voltage source (Vdd), and providean output indicative of a characteristic of the multiple samples, suchas a peak voltage detected. As used herein, a “measurement stage”includes the portion of the measurement circuit that detects the peakself-capacitance or the peak mutual capacitance over a measurement cyclefor a given electrode or electrode pair. In the embodiment illustratedin FIG. 19, there are eight measurement stages, each corresponding toone of the measurement capacitors (Ce1, Ce2 . . . Ce8). Each of themeasurement stages is configured to operate in the same manner; however,it should be understood that one or more measurement stages may beconfigured differently from another of the measurement stages. Forexample, one measurement stage may be configured as depicted in theillustrated embodiment, and another of the measurement stages may beconfigured according to another of the illustrated embodiments.

Each of the measurement stages may be selectively coupled to asample/hold capacitor (Cadc), similar to the sample/hold capacitor(Cadc) in the illustrated embodiment of FIG. 15. For example, an outputfrom a measurement stage may be selectively provided to the sample/holdcapacitor (Cadc), while outputs from the remaining measurement stagesare effectively disconnected from the sample/hold capacitor (Cadc). Thisconfiguration may prevent interference between measurement stages, andenable the signal processing circuitry to obtain an accurate measurementof each output provided to the sample/hold capacitor. Discharging of thesample/hold capacitor (Cadc) may be achieved via the discharge switch(SwA), similar to the discharge switch (SwA) in the illustratedembodiment of FIG. 15.

In the illustrated embodiment, the voltage source (Vdd) may generatemultiple samples for each measurement electrode (Ce1, Ce2 . . . Ce8),and for respective assessment by each of the measurement stages. Thecontroller may control which output of the measurement stages isprovided to the signal process circuitry, thereby enabling the signalprocess circuitry to evaluate the output and determine whether a “touch”is present in proximity to one or more of the electrode sensing element(Ce1, Ce2 . . . Ce8).

Each of the measurement stages may operate in a manner similar to themeasurement circuitry of the illustrated embodiment of FIG. 15. In otherwords, each of the measurement stages may include a peak detectorincluding peak detector diode (Ds), a peak detector capacitor (Cs) and agate switch (SwB). With this configuration, the diodes (Ds1, Ds2 . . .Ds8) and the peak detector capacitors (Cs1, Cs2 . . . Cs8) may assessmultiple samples generated by the voltage source (Vdd) in order toidentify a peak voltage of the multiple samples. This peak voltage maybe supplied as an output of the measurement stage. It should beunderstood that each of the measurement stages may be configureddifferently according to one or more embodiments described herein.

Each of the measurement stages in the illustrated embodiment may includea discharge switch (SwD1, SwD2 . . . SwD8), similar to the dischargeswitch (SwD) in the illustrated embodiment of FIG. 15, that is capableof discharging parasitic capacitance seen by the electrode sensingelements (Ce1, Ce2 . . . Ce8). As discussed herein, adverse effects dueto presence of parasitic capacitance may be reduced or eliminated usingthis configuration. Additionally, or alternatively, a load resistor (RL)may be included to discharge parasitic capacitance. Further, the loadresistor (RL) may be used to provide a lower impedance path or toattenuate the output of the drive circuit.

FIG. 21 illustrates an electrical schematic and block diagram of acapacitive touch sensor in accordance with a seventh embodiment. Timingdiagrams associated with one or more operational states of theillustrated embodiment are shown in FIGS. 22-24. The capacitance touchsensor is similar to the capacitance sensor described in connection withthe illustrated embodiment of FIG. 15, but with one primaryexception—though it should be understood that the capacitance sensor ofFIG. 21 may be configured to include further exceptions according to oneor more embodiments described herein.

In particular, the capacitance touch sensor of FIG. 21 includes a drivecircuit and signal processing circuitry, both of which are similar tothe drive circuit and the signal processing circuitry of FIG. 15. Thecapacitance touch sensor of FIG. 21 may also include a measurementcircuit similar to the measurement circuit of FIG. 15, but including atransistor-based sensor electrode or a mutual inductance type sensorelectrode substantially as set forth above in connection with FIG. 9.Although illustrated as including a transistor-based sensor electrode ora mutual inductance type sensor electrode, it should be understood thatthe present application is not so limited, and may includeconfigurations having one type of sensor electrode. Other than thedifference in sensor electrode type, the measurement circuit of FIG. 21includes the same components as the measurement circuit of FIG. 15described herein. The measurement circuit of FIG. 21 may be incorporatedinto one or more or all of the measurement stages described inconnection with FIG. 19.

FIG. 25 illustrates an electrical schematic and block diagram of acapacitive touch sensor in accordance with an eighth embodiment. In theillustrated embodiment of FIG. 25, an electrical schematic and blockdiagram of a multi-electrode capacitance sensor or an array-typecapacitance sensor is shown. A timing diagram associated with one ormore operational states of the illustrated embodiment are shown in FIG.26. The capacitive touch sensor is similar to the capacitive touchsensor of FIG. 21, but has been configured to sense multiple capacitiveelectrodes. In particular, the sensor of FIG. 25 includes measurementcircuitry configured to assess multiple samples generated by drivecircuitry, and to provide an output indicative of the multiple samplesto signal processing circuitry. The measurement circuitry includesseveral measurement stages, each associated with a sensor electrodedriven by the drive circuitry. The components incorporated into thecapacitance sensor are nearly the same as the capacitance sensor, withthe exception of including a transistor-based sensor electrode or amutual inductance type sensor electrode configuration described inconnection with the illustrated embodiment of FIG. 21.

FIG. 27 illustrates a circuit diagram of a capacitive touch sensor inaccordance with a ninth embodiment. Timing diagrams associated with oneor more operational states of the capacitive touch sensor of FIG. 27 areshown in FIGS. 28 through 30. The capacitive touch sensor of FIG. 27 issimilar to the capacitive touch sensor of FIG. 15, except that the peakdetector diode (Ds) is replaced with a peak detector switch (SwC).Unlike the peak detector diode (Ds), the peak detector switch (SwC) doesnot automatically turn on or off. That is, the peak detector diode (Ds)automatically transitions between conducting and non-conducting statesin dependence on the voltage drop across the anode and cathode of thediode (Ds). The peak detector switch (SwC) enables control over whethervoltage is applied to a peak detector capacitor (Ca) under circumstancesdifferent from that of the peak detector diode (Ds). For example, thepeak detector switch (SwC) may be activated by the controller duringtimes at which the peak detector diode (Ds) would be deactivated, andconversely, the peak detector switch (SwC) may be deactivated duringtimes at which the peak detector diode (Ds) would be activated.

FIG. 31 illustrates a circuit diagram of a capacitive touch sensor inaccordance with a tenth embodiment. FIG. 32 illustrates a timing diagramassociated with one or more operational states of the capacitive touchsensor of FIG. 31. The capacitive touch sensor of FIG. 31 is similar tothe capacitive touch sensor of FIG. 27, except that the capacitive touchsensor of FIG. 31 includes eight measurement stages corresponding toeach of eight measurement electrodes (Ce1, Ce2 . . . Ce8). Eachmeasurement stage includes the components of the measurement circuit ofFIG. 31 above, including eight peak detector switches (SwC1, SwC2 . . .SwC8). As noted above, the measurement stage includes the portion of themeasurement circuit that detects the peak self-capacitance or the peakmutual capacitance for a given electrode or electrode pair. In theembodiment illustrated in FIG. 31, there are eight measurement stages,each corresponding to one of the measurement capacitors (Ce1, Ce2 . . .Ce8). Each measurement stage is coupled to the sample-and-hold capacitor(Cadc), which provides a DC output to the signal processing circuit asnoted above.

FIG. 33 illustrates a circuit diagram of a capacitive touch sensor inaccordance with an eleventh embodiment. Timing diagrams associated withone or more operational states of the capacitive touch sensor of FIG. 33are shown in FIGS. 34 through 36. The capacitive touch sensor of FIG. 33is similar in structure and function to the capacitive touch sensor ofFIG. 27, except the dual-electrode measurement capacitor (Ce) formeasurement mutual capacitance is replaced with a transistor-controlledelectrode for measuring self-capacitance. In particular, a PNPtransistor (Q) includes an emitter that is coupled to the voltage source(Vdd), a base coupled to a resistor (Rbe), and a collector coupled tothe peak detector switch (SwC). In operation, the measurement electrode(Ce) and the resistor (Rbe) form a delay network. For example, thestimulus voltage causes a voltage to develop between the emitter and thebase of the PNP transistor (Q), causing a base current to flow. Thiswill in turn cause collector current to flow that is proportional to thegain of the transistor (Q). If the capacitance of the measurementcapacitor (Ce) increases due to a stimuli, for example a touch input,the collector current will increase, which will charge the peak detectorcapacitor (Cs) for a give pulse of stimulus.

FIG. 37 illustrates a circuit diagram of a capacitive touch sensor inaccordance with a twelfth embodiment. FIG. 38 illustrates a timingdiagram associated with one or more operational states of the capacitivetouch sensor of FIG. 37. The capacitive touch sensor of FIG. 37 issimilar to the capacitive touch sensor of FIG. 33, except that thecapacitive touch sensor of FIG. 37 includes eight transistor-controlledelectrodes (Ce1, Ce2 . . . Ce8) and eight measurement stages. Eachmeasurement stage includes the components of the measurement circuit ofFIG. 33 above, including eight peak detector switches (SwC1, SwC2 . . .SwC8). Each measurement stage detects the peak self-capacitance for acorresponding transistor-controlled electrode (Ce1, Ce2 . . . Ce8). Eachmeasurement stage is coupled to the sample-and-hold capacitor (Cadc),which provides a DC output to the signal processing circuit as notedabove.

FIG. 39 illustrates a circuit diagram of a capacitive touch sensor inaccordance with a thirteenth embodiment. Timing diagrams associated withone or more operational states of the capacitive touch sensor of FIG. 39are shown in FIGS. 40 through 42. The capacitive touch sensor of FIG. 39is similar in structure and function to the capacitive touch sensor ofFIG. 33, except the voltage source (Vdd) is coupled to the peak detectorcapacitor (Cs), which is connected in parallel to the measurementcapacitor (Ce). The voltage at the sample-and-hold capacitor (Cadc) isproportional to the capacitance at the measurement capacitor (Ce), whichis then output to the signal processing circuit for digital signalprocessing. FIG. 43 illustrates a circuit diagram of a capacitive touchsensor in accordance with a fourteenth embodiment. FIG. 44 illustrates atiming diagram associated with one or more operational states of thecapacitive touch sensor of FIG. 43. The capacitive touch sensor of FIG.43 is similar to the capacitive touch sensor of FIG. 39, except that thecapacitive touch sensor of FIG. 43 includes eight electrodes (Ce1, Ce2 .. . Ce8) and eight measurement stages. Each measurement stage includesthe components of the measurement circuit of FIG. 39 above, includingeight peak detector switches, and each measurement stage detects thepeak self-capacitance for a corresponding measurement electrode (Ce1,Ce2 . . . Ce8). Each measurement stage is coupled to the sample-and-holdcapacitor (Cadc), which provides a DC output to the signal processingcircuit as noted above.

FIGS. 45-48 include physical constructions for electrode structures fora capacitive touch sensor. In particular, the electrode structure ofFIGS. 45 and 46 can be used in connection with the capacitive touchsensors of any of FIGS. 3-8, 21-26, and 33-38. The stimulus signalsurrounds each of the electrodes (Ce1, Ce2 . . . Ce8) with traces thatlead back to the edge of a sensor board, where the signals would beprocessed as described above. The electrode structure of FIG. 47 can beused in connection with the capacitive touch sensors of any of FIGS.9-14, 21-26, and 33-38. The transistors may be located on the tail ofthe circuit or off the sensor board as shown in FIG. 47. The closer tothe electrode that the transistors are located the better the isolationfrom parasitic capacitance, while also preventing cross coupling. Theelectrode structure of FIG. 48 can be used in connection with thecapacitive touch sensors of any of FIGS. 9-14, 21-26 and 33-38. Thestimulus is connected to an outer electrode that substantially surroundsthe measurement electrodes (Ce1, Ce2 . . . Ce8). This configuration canprovided better isolation between the measurement electrodes (Ce1, Ce2 .. . Ce8), thereby increasing water immunity. The transistors may also belocated on the tail of the circuit or off the sensor board as shown inFIG. 47. The closer to the electrode that the transistors are locatedthe better the isolation from parasitic capacitance, while alsopreventing cross coupling.

FIG. 49 illustrates a circuit diagram of a capacitive touch sensor inaccordance with a fifteenth embodiment. In the illustrated embodiment ofFIG. 49, the transistor-based sensor electrode is atransistor-transistor type sensor. The transistor-transistor type sensorincludes an NPN transistor that may aid in providing water immunity andisolation. In this configuration, if the signal output from thetransistor-transistor type sensor is insufficient to obtain asatisfactory signal, an amplification stage may be included to increasethe gain on the output signal. The amplification stage may be one ofseveral different amplification topologies. In the illustratedembodiment, a PNP transistor is used as part of an amplification stage.The collector current of the NPN transistor may provide base current forthe PNP transistor, which in turn amplifies and increases the spacecurrent by the gain of the PNP transistor at the collector of the PNPtransistor. The signal output at the collector of the PNP transistor maybe assessed using any of the configurations or embodiments describedherein. In the illustrated embodiment, the measurement circuit of FIG.49 is configured similar to the measurement circuit of FIG. 27, but itshould be understood that the measurement circuit of FIG. 49 may beconfigured differently.

The capacitive touch sensors shown above are described in connectionwith a Time Domain Differential Processing Circuit, while measuringmultiple electrodes simultaneously. The capacitive touch sensorsdescribed above can be used with other capacitive measuring techniques,including those that rely on a comparison against a predeterminedthreshold. Even though not shown in all of the Figures, any of theinputs to the analog-to-digital converters can be preceded by anamplifying stage to increase the gain and thereby reduce the processingrequirements of the signal processing circuit. While the Figuresillustrate one stimulus line driving eight sensing return lines, theFigures do not limit the present invention to these configurations. Forexample, there can be multiple stimulus lines forming several drive rowswith additional electrodes, with the electrodes forming a column and rowmatrix. For example, each additional drive line may be turned on and offperiodically to allow the sensing columns to simultaneously process eachdrive row, sampling each row, and simultaneously sensing the outputsfrom each row's electrodes.

The above description is that of current embodiments. Variousalterations and changes can be made without departing from the spiritand broader aspects of the invention as defined in the appended claims,which are to be interpreted in accordance with the principles of patentlaw including the doctrine of equivalents. This disclosure is presentedfor illustrative purposes and should not be interpreted as an exhaustivedescription of all embodiments of the invention or to limit the scope ofthe claims to the specific elements illustrated or described inconnection with these embodiments. For example, and without limitation,any individual element(s) of the described invention may be replaced byalternative elements that provide substantially similar functionality orotherwise provide adequate operation. This includes, for example,presently known alternative elements, such as those that might becurrently known to one skilled in the art, and alternative elements thatmay be developed in the future, such as those that one skilled in theart might, upon development, recognize as an alternative. Further, thedisclosed embodiments include a plurality of features that are describedin concert and that might cooperatively provide a collection ofbenefits. The present invention is not limited to only those embodimentsthat include all of these features or that provide all of the statedbenefits, except to the extent otherwise expressly set forth in theissued claims. Any reference to claim elements in the singular, forexample, using the articles “a,” “an,” “the” or “said,” is not to beconstrued as limiting the element to the singular. Any reference toclaim elements as “at least one of X, Y and Z” is meant to include anyone of X, Y or Z individually, and any combination of X, Y and Z, forexample, X, Y, Z; X, Y; X, Z; and Y, Z.

1. A method comprising: strobing one of a first and second electrodeshaving a mutual capacitance with a time-varying waveform over a firstmeasurement period; strobing one of the first and second electrodes witha time-varying waveform over a second measurement period; electricallycoupling a processing unit to the first and second electrodes, theprocessing unit configured to register a first touch signature inresponse to an object approaching one of the first or second electrode,the first touch signature occurring over a total time domain (T) betweena first time and a second time, between a first substantially constantmutual capacitance and a second substantially constant mutualcapacitance, wherein the first touch signature includes a rate of change(ds/dt) of the mutual capacitance in combination with at least one ofthe following parameters of the first touch signature: an intervalchange in mutual capacitance (ds) during the total time domain (T),wherein the interval change in mutual capacitance (ds) is less than atotal change in mutual capacitance (S) for the first touch signature, aninterval time domain (dt) corresponding to the interval change in mutualcapacitance (ds), wherein the interval time domain (dt) is less than thetotal time domain (T) for the first touch signature.
 2. The method claim1, further comprising operatively coupling an A/D converter to the firstelectrode, wherein the first electrode is a sense electrode.
 3. Themethod claim 1, further comprising operatively coupling a capacitor tothe first electrode, wherein the first electrode is a sense electrode.4. The method according to claim 1 wherein the second electrode is oneof a plurality of second electrodes.
 5. The method according to claim 4wherein the first electrode is common to the plurality of secondelectrodes.
 6. The method according to claim 4 wherein the plurality ofsecond electrodes are arranged in an array.
 7. The method according toclaim 1 further comprising providing a third electrode configured toprovide stimulus to the first and second electrodes.
 8. The methodaccording to claim 1 further comprising calculating one of ds, dt,ds/dt, S, T, and combinations thereof.
 9. The method according to claim1 further comprising disposing a substrate in proximity to the first andsecond electrodes, and calculating a substrate relative movement. 10.The method according to claim 9 further comprising calculating asubstrate relative movement is calculating the movement of a ridgedsubstrate.
 11. The method according to claim 9 further comprisingcalculating a substrate relative movement is calculating the multistagemovement of a flexible substrate.
 12. The method according to claim 7wherein the third electrode provides stimulus to one of the first andsecond electrodes selected from the group consisting of ground, v−, v+,a periodic signal and combinations thereof.
 13. The method according toclaim 1 further comprising calculating measurement of one of ds, dt,ds/dt, S, T, and combinations thereof at one of the first and secondelectrodes.
 14. The method according to claim 13 further comprisingfiltering the signal prior to calculating measurement of one of ds, dt,ds/dt, S, T, and combinations thereof from a first electrode.
 15. Themethod according to claim 13 further comprising filtering the signalprior to calculating measurement of one of ds, dt, ds/dt, S, T, andcombinations thereof from the first and second electrodes.
 16. Themethod according to claim 1 further comprising providing one of ahardware filter and a software filter.
 17. The method according to claim1 further comprising conducting a first signature profile decision basedon if ds is less than a first value for a given dt, too determined to bea touch event did not occur.
 18. The method according to claim 17further comprising conducting a second signature profile decision basedon if ds is greater than a second value for a given dt, too determinedto be a touch event did not occur.
 19. The method according to claim 1wherein calculating differential measurement of one of ds, dt, ds/dt, S,T, and combinations thereof is done simultaneously.
 20. The methodaccording to claim 1 further comprising disposing the first and secondof electrodes in multiple planes above a substrate.